The present invention relates generally to fiber optic rotary joints and, more particularly, to contactless fiber optic rotary joints for transmitting high bit-rate signals. Even more particularly, the present invention relates to a segmented waveguide used in assembling a fiber optic rotary joint and for use in retrofitting an existing cat-scan gantry with a fiber optic rotary joint.
Devices called fiber optic rotary joints allow optical signals to be transferred between fibers located on rotating and stationary members. The device is categorized as an on-axis rotary joint when the fibers are located along the axis of rotation. The device is categorized as an off-axis rotary joint if access to the axis of rotation or centerline is not possible. The technology employed in these two types of rotary joints is quite different. The present invention concerns off-axis rotary joints.
Contactless fiber optic rotary off-axis joints have been developed as disclosed in U.S. Pat. No. 4,525,025 to the present assignee. The ""025 patent discloses a fiber optic rotary joint which couples a pulsed optical signal across a rotary interface and includes an annular reflective wall formed on a stator and an optic fiber mounted on the stator having one end in close proximity and tangential to the annular reflective wall. A signal emitted by one of the optic fibers will be reflected along the annular reflective wall and received by the other of the optic fibers.
Actual joints constructed in a manner similar to that generally disclosed in the ""025 patent have been limited to a rotor diameter of 10-12 inches and data rates of 50 megabits/sec. due to unacceptable propagation delays causing bit pulse-width distortion. There is a need for joints having rotor diameters of 40-50 inches using pulsed optical signals having data transfer rates of 1-3 gigabits/sec. To meet these requirements, two criteria must be met. First, optical variations with rotation must be minimized. Second, propagation delays must be controlled to minimize effect on bit pulse-width distortion.
Optical variations with rotation can be minimized by using a multiplicity of optical pick-ups spaced circumferentially. The problem is that it is desirable to have as few pick-ups as possible to minimize complexity and cost.
Propagation delays must be controlled. For example, consider a waveguide that is fonned into a continuous 360xc2x0 arc that is four meters in circumference. If four fiber optic pick-ups located equidistant around the circumference are focused to a common photodiode and a single light source is used to inject a signal into a waveguide at a point of injection, then the optical pick-up that is nearest to the point of injection will receive the transmitted signal first and thereby transmit the received signal to the photodiode first. Because the second optical pick-up is located 90xc2x0 away, the optical signal travelling from the point of injection at a speed of three ns/meter will arrive at the second pick-up three ns after the first. Similarly, the third pick-up would receive the transmitted signal after nine ns. Thus, for a four meter circumference continuous waveguide, a propagation delay of twelve ns would result. For a 100 Mb/s signal, which has a 10 ns bit width to be transmitted under these conditions, the bit shape would be distorted by signals arriving at the different optical pick-ups at different times because the propagation delays are larger than the bit width. A larger diameter joint exacerbates the problem and would exhibit even larger delays.
Other difficulties can be encountered when installing a fiber optic rotary joint in, for example, a cat-scan machine. The difficulty with such an arrangement is that the joint is pre-assembled including the rotor and the stator at a factory and then often needs to be dissembled when installed in the gantry of an existing cat-scan machine. It is desirable to reduce the effort and cost to install the fiber optic rotary joint in the cat-scan machine.
Another problem is that it is difficult, expensive and time consuming to install a waveguide for a stator and the various optical transmitters and receivers required to form a fiber optic rotary joint.
It is, therefore an object of the present invention to provide a fiber optic rotary joint which can transmit a high bit-rate signal.
It is another object of the present invention to provide a fiber optic rotary joint capable of having a circumference of at least 4 meters.
It is yet a further object of the present invention to provide a segmented waveguide which can be used to retrofit an existing gantry to form a fiber optic rotary joint.
It is yet another object of the present invention to provide a method of retrofitting a gantry with a fiber optic rotary joint.
These and other objects of the present invention are achieved by a segmented waveguide for a fiber optic rotary joint, the fiber optic rotary joint includes a rotor and an existing stator surface, the rotor having one of a plurality of light transmitters and light receivers connected to a first circumference of the rotor, a segmented waveguide mountable to the existing stator surface, a segmented waveguide capable of reflecting optical energy transmitted from the plurality of light transmitters on the rotor, the rotor rotatable through a full 360xc2x0 and concentric to the existing stator surface. A reflective waveguide surface is shaped to match a portion of the exiting stator surface. At least one waveguide support supports the reflective waveguide surface and connects to the existing stator and at least one of a light transmitter or light transmitter optically couples to the reflective waveguide surface.
These and other objects of the present invention are achieved by a waveguide section mountable in an existing circular bore. The reflective waveguide surface extends up to a 135xc2x0 arc of the existing circular bore. The waveguide section supports structure for mounting a reflective waveguide surface in the existing circular bore and includes one of a light transmitter and a light receiver.
These and other objects of the present invention are a method of retrofitting an existing gantry with a fiber optic rotary joint, securing at least one reflective waveguide surface to an inner diameter of the existing gantry, securing one of a light transmitting device and light receiving device to the reflective waveguide, securing a plurality of light transmitters or light receivers to a rotor positioned concentrically in the gantry.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive.